Air boost systems, such as turbochargers and superchargers, have long been used to increase engine power in many applications including powering on-highway trucks, boats, large ships and, more recently, automobiles. In general, engine power is linked to engine displacement. Thus, a significant increase in power generally requires designing and fabricating a more expensive engine that is significantly larger and heavier. Air boost systems that are smaller and lighter can provide the same increase in engine power at a lower cost. The design and function of turbochargers is described in detail in the prior art, for example, U.S. Pat. Nos. 4,705,463, 5,399,064, and 6,164,931, the disclosures of which are incorporated herein by reference. The design and function of superchargers is also described in the prior art, for example, U.S. Pat. Nos. 4,530,338 and 4,991,562, the disclosures of which are incorporated herein by reference.
Air boost systems include a compressor stage that is upstream of the engine intake manifold. The compressor stage includes a compressor housing, which has an inlet and an outlet, and encloses a compressor rotor. The compressor rotor is attached to a shaft that is typically driven either by the engine, in the case of a supercharger, or by exhaust gas from the engine, in the case of a turbocharger. As the compressor rotor rotates, it increases the mass flow rate and pressure of the air entering the engine. Since the same volume of air at a higher pressure contains more oxygen per volume than ambient air, the air boost system enables to engine to combust more fuel, thereby generating more power, for a given engine displacement.
Rotating at speeds of up to 300,000 RPM and designed to operate for 200,000 and more miles, the compressor stage handles extremely large volumes of air. Air drawn from the atmosphere into the compressor contains very fine particles such as dust, pollen, oil, smoke, dirt, and other contaminants. Although filters are commonly used to clean the air, even the best filters cannot completely prevent particles from entering the compressor and producing deposits on the compressor rotor, compressor housing, intercooler, downstream piping, and other downstream components. This problem of deposits accumulating on air boost system components is referred to as fouling.
The problem of compressor side fouling has been aggravated in recent years as a result of the evolving awareness of the impact of engine emissions on the environment. This awareness led to the development of closed crankcase ventilation systems that recycle engine gases instead of venting blow-by to the atmosphere. The closed crankcase ventilation systems filter the engine gases and reintroduce them upstream of the compressor. Even after the blow-by has been filtered it may still contain oil vapor and other contaminants that result in fouling on the air boost system components.
In the initial phase of the fouling problem, an increased surface roughness of the compressor rotor may affect the behavior of the boundary layer air interacting with the rotor. As the airflow through the compressor stage becomes more turbulent and the compressor become less efficient. This inefficiency causes an increase in fuel consumption and a loss in power generation output.
Government mandated improvements in fuel economy, power ratings and emissions performance for engines, and particularly for commercial diesel applications, has resulted in a need for air boost systems capable of producing increased pressure ratios. This compounds the problems outlined above in two ways. First, the increased pressure ratios require increased mass flow rates thereby increasing the mass of contaminants that pass through the air boost system. Second, maintaining high efficiencies is critical to achieving the elevated pressure ratios.
It is therefore necessary to remove fouling from the air boost system to deliver air at the optimal pressure to the engine. It is known to remove fouling from the air boost system by removing and disassembling the air handling system and then scraping the deposits off of the system components. However, this method of cleaning is expensive in terms of both labor costs and vehicle down time.
Methods have been developed for wet cleaning of the nozzle rings of an exhaust-gas turbocharger turbine by injecting cold water immediately upstream of the nozzle rings and thermally shocking the contaminants. For example, U.S. Pat. No. 5,944,483, entitled “Method and Apparatus for the Wet Cleaning of the Nozzle Ring of an Exhaust-Gas Turbocharger Turbine” to Beck at al. However, this method requires maintenance of a separate cleaning system and relies predominantly on thermal shock to achieve cleaning. Unlike the turbine stage of a turbocharger, portions of the compressor stage of an air boost system, particularly the intercooler and piping downstream of the intercooler, are not hot enough to rely on thermal shock for contaminant removal. Thus, it is desirable to develop a device and method for cleaning air boost systems that is inexpensive, that does not rely on thermal shock cleaning, and that does not require vehicle down time or a separate cleaning system.
Systems have been developed for cleaning the turbine blades of a turbocharger by supplying atomized water under high pressure to the exhaust gas powering the turbocharger. For example, U.S. Pat. No. 4,548,040, entitled “Method and Apparatus for Determining When to Initiate Cleaning of Turbocharger Turbine Blades” to Miller et al. Like the method of cleaning nozzle rings above, the Miller approach require maintenance of a separate cleaning system and cleans the turbine stage where water and elevated temperatures make thermal shock cleaning effective. Thus, it is desirable to develop a device and method for cleaning air boost systems that is inexpensive, that does not rely on thermal shock cleaning, and that does not require vehicle down time or a separate cleaning system.
The need to find a simple, low-cost device or method of maintaining air boost system efficiency is particularly pronounced in some engine markets, such as the automobile market. Since space under the hood is at a premium in the automobile market, one would expect to see extensive use of air boost systems in the automobile market. However, experience tells us that this is not the case. Unlike markets such as the trucking industry and the shipping industry where air boost systems are commonplace, the majority of automobile consumers are extremely sensitive to initial vehicle costs, maintenance costs, and vehicle down time. Because of these issues, automobiles with air boost systems are generally limited to high-end cars and sports cars where the consumer is willing to deal with the present drawbacks in exchange for performance. Thus, in order for the masses to reap the benefits of air boost systems, it is desirable to develop an inexpensive device or method for cleaning air boost systems that is simple to maintain, small enough to fit under the hood of current automobiles, and avoids taking the vehicle out of service.